-LRB- CNN -RRB- Imran Khawaja left London to train with a terror group in Syria last year and rose in the ranks , eventually appearing in one of its online promotional videos holding a severed head to the camera , authorities say .

Sometime later , the group announced he was dead -- but police say it was only a ruse , uncovered when he was arrested trying to re-enter the United Kingdom .

Khawaja , 27 , was sentenced Friday in Woolwich Crown Court to 12 years in prison , having pleaded guilty to preparing acts of terrorism and other terror-related charges , London 's Metropolitan Police said .

`` Khawaja chose to become a terrorist , engaged in weapons training in a terrorist training camp and faked his own death in order to conceal his entry back into the UK , '' Metropolitan Police counterterrorism Cmdr. Richard Walton said Friday . `` This sentence sends a powerful message to those who plan or prepare acts of terrorism overseas or here in the UK . ''

Authorities say Khawaja , of west London , traveled to Syria in January 2014 and joined Rayat al Tawheed , a group aligned with ISIS , the brutal terror group that has captured parts of Syria and Iraq for what it says is its Islamic caliphate .

Eventually , he took the name Abu Daigham al-Britani and appeared in one of the group 's promotional videos featuring the training camp and encouraging others to join it , police said .

In a separate video posted on social media , police say , a man with his face covered is seen with a bag of severed heads . He picks up one of the heads , according to police , and shows it to the camera .

Police say a description with the video reads : `` British ISIS fighter Abu Daigham al-Britani with Government soldier 's head Syria . ''

In May , the group sent a message on social media claiming that Abu Daigham al-Britani had been killed -- news reported at the time by the British media .

Khawaja , however , was arrested on June 3 after entering the United Kingdom at the port city of Dover , Metropolitan Police said .

`` The images and video of Khawaja in Syria are horrific and deeply disturbing . He was a senior figure in Rayat al Tawheed , a group aligned to the Islamic State terrorist group that celebrated its terrorist acts through social media back to the UK , '' Walton said .

Arrested with Khawaja was his cousin Tahir Bhatti , 45 , on suspicion of assisting an offender . Police said they searched addresses linked to both men , and found messages and photographs that showed Khawaja had engaged in terrorist training in Syria , including how to handle weapons .

Khawaja pleaded guilty in December to preparation of acts of terrorism , attending a terrorist training camp , weapons training and possession of an article for terrorist purposes .

Bhatti pleaded guilty last month to assisting an offender and was sentenced Friday to 21 months in prison , Metropolitan Police said .

A second man accused of helping Khawaja , Asim Ali , 33 , of west London , was arrested in August . He was accused of , among other things , giving Khawaja money before Khawaja left for Syria .

Ali pleaded guilty in December to entering a funding arrangement for the purposes of terrorism . He was sentenced Friday to 21 months in prison , Metropolitan Police said .

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Police say Imran Khawaja , of west London , trained with a terror group in Syria last year

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He was in a promotional video showing him holding a severed head , police say

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The terror group said he 'd died , but he really was trying to return to the UK , where he was arrested , police say